Background. An estimated 40 of persons younger than 50 years who are hospitalized for a thrombotic episode have an identifiable, inherited thrombophilia, a condition that increases their tendency to form a blood clot. Identifying an inherited thrombophilia in an individual could be beneficial as it may improve understanding about the etiology of the disease, allow for prevention in family members and influence disease management. In order to optimize genetic testing for thrombophilia, genetic counselors play a vital role in assessing appropriateness for testing, educating individuals about genetic testing and risks, and coordinating care among health care professionals. Objectives. This study examined genetic counselors' knowledge and comfort levels in counseling patients for hereditary thrombophilia. Findings from this study will be used to better understand what kind of learning tool would be beneficial to educate genetic counselors about the topic of hereditary thrombophilia. Methods. Eligible study participants consisted of genetic counselors that belong to the National Society of Genetic Counselors (NSGC) ListServe, an electronic mail service to which members voluntarily subscribe. Participants were directed through an electronic link to an online survey. Results. Of the 1,560 genetic counselors that subscribe to the NSGC Listserve 169 (10.8 ) responded to our invitation to participate. A statistically significant association was found between comfort level questions asked of the respondents and their knowledge on the topic (P=.041, <.001, .018, .029 and .125). Genetic counselors' experience with counseling patients for hereditary thrombophilia was statistically significant (P=<.001) as well while area/s of specialty [prenatal: P=.258; pediatric: P=.434; cancer: P=.897; adult: P=.659; specialty disease: P=.348; screening (multiple marker): P=.437; infertility (ART/IVF): P=.748, etc.] and years of experience (P= .619) were not found to be statistically significant in relation to the respondents' knowledge on the topic of hereditary thrombophilia.